With immunoperoxidase staining, cell types of developing and adult rat and human hypophyses will be examined for the marker enzyme suggesting neuroectodermal provenance, neuron-specific enolase. The normal adult human hypophysis will be investigated immunocytochemically for functional heterogeneity of gamma cells, response of gonadotrophs to cessation of ovarian function, and the cellular localization of the opioid peptides beta-endorphin and met-enkephalin. A postulated acidophilic "stem" cell (containing both growth hormone and prolactin) will be sought in normal and adenomatous pituitaries. The function of pars nervosa "basophils" will be studied by correlation of immunocytology with assays for ACTH-related peptides. Adenomas producing prolactin, growth hormone or both will be investigated by electron microscopic immunocytochemistry. With a battery of antibodies against a variety of pituitary hormones, adenomas found at autopsy or removed surgically will be surveyed for the prevalence of multihormonal neoplasms.